1. Field of the Invention
This invention relates to attitude meters for determining the orientation of a surface with respect to the direction of magnetic North and a horizontal plane.
2. Discussion of the Prior Art
Attitude meters for indicating the orientation of a surface with respect to magnetic North and a horizontal plane are known in the art. Such meters find a variety of applications as for example, construction, exploration and mining (principally for determining strike and dip), surveying, and navigation. In an attempt to obtain greater accuracy while reducing the cost of complicated gyroscopically stabilized platforms, it is known to employ liquid supported floating indicators within spherical transparent globes such as disclosed in U.S. Pat. Nos. 1,294,710 to Roland issued Feb. 18, 1919 and 1,376,727 to Pentz et al issued May 3, 1921. While such meters are suitable for the purposes disclosed, difficulty arises by virtue of the indicia inscribed on the outer surfaces of spherical globes since such indicia tend to obstruct a clear view of the floating indicator especially at the pole or top of the sphere. Obstruction of view becomes a specially difficult problem where great accuracy is desired since a large number of inscribed indicia lines must be used. Also, the instrument's accuracy is limited by the number of lines that can by physically inscribed on the spherical surface.
An alternative to the use of inscribed indicia is disclosed in U.S. Pat. No. 1,009,832 to Curtiss issued Nov. 28, 1911, wherein arched bands mounted within a transparent casing cooperate to indicate the angular position of a base. However, the arched bands disclosed in the Curtiss patent fail to simultaneously indicate the orientation of the base both with respect to a horizontal and a vertical direction in a manner which is easily read since the arches are both mounted within the casing requiring angles oblique to the gimballed supports to be read from both scales. Curtiss makes no suggestion as to how the arched bands might be employed in a float type attitude meter so as to enable more accurate visual readings.
While float type meters enjoy a substantial cost advantage over geometric instruments employing complicated gimballed supports, certain inaccuracies may result unless frictional contact is prevented between the float and the casing of the float type meter. One attempt to solve this problem has been to provide a bearing for the float having sufficiently low frictional characteristics so as not to interfere with the accuracy of the output readings while at the same time permitting limited universal movement of the meter. Such bearings are often characterized by a central opening in a floating compass disk to permit a fixed bearing rod to be inserted therethrough. Examples of such bearings are disclosed in U.S. Pat. Nos. 1,754,055 to Senter issued Apr. 8, 1930 and 3,585,728 to Ogg issued June 22, 1971. The utility of such bearings has been impaired in the past by the need to enlarge the central opening of the disk sufficiently to accommodate limited universal motion of the compass about the fixed rod. Also, none of the prior art instruments discussed above provides a single structural means for automatically pointing to the precise direction of inclination.